The polyphenol silybin has anti-oxidant and anti-cancer properties. The poor bioavailability of some polyphenols (flavonoids, and terpenoids) can be improved by binding them to phosphatidylcholine (phytosome technology). Many studies have focused on the most common phytosome, silybin-phosphatidylcholine, particularly for its hepatoprotective effects. However, in recent years, studies have also been conducted to determine its anti-cancer effect. Considering that the serum starvation should not be used for studies that are not focused on cell cycle arrest, we studied the effect of silybin-phosphatidylcholine from Silybin Advanced™ in 1:2 ratio (one part silybin bound to two parts phosphatidylcholine) on HER2 gene expression on the SKBR3 breast cancer cell line which were cultured in complete medium (not serum deprivation). The results were compared with our previous study of silybin on HER2 expression on SKBR3 cells. An MTT test was used to determine concentrations for cell treatment, and the gene expression was defined by real-time RT-PCR.Outcomes showed significant concentration- and time-dependent cell growth inhibitory effects of silybin, and silybin-phosphatidylcholine and HER2 down regulation on SKBR3 cells. Silybin-phosphatidylcholine concentrations had a much larger inhibitory and HER2 down regulate effect on cell growth than the same silybin concentrations on SKBR3 cells.